The present invention relates generally to air conditioning systems for vehicles, and more particularly to air conditioning systems with thermal storage and evaporator temperature control.
The use of conventional air conditioning systems in vehicles reduces the fuel economy of the vehicles. Given the desire to improve the fuel economy of automotive vehicles, various systems have been employed in an attempt to reduce the fuel economy penalty caused by the air conditioning system. Some air conditioning systems employ variable capacity refrigerant compressors to adjust system capacity to cooling demands and thus improve fuel economy. However, for some automotive vehicles, variable capacity compressors may be impractical due to cost or for other reasons. These other types of air conditioning systems typically employ a fixed capacity compressor that is driven by the engine, with a compressor clutch cycled on and off to switch between full compressor capacity and zero compressor capacity.
Conventionally, for fixed capacity, belt driven compressors, the compressor on/off cycling is based on a fixed temperature or pressure of the refrigerant that maintains the evaporator temperature a few degrees above the freezing point of water. This provides maximum cooling and dehumidification while preventing evaporator icing. Then if the air exiting the evaporator is too cold for the demand in the passenger compartment, a portion of the cooled air is directed through the heater core to be re-heated. Operating at maximum cooling of the air with subsequent reheating is an inefficient way to operate the air conditioning system. Consequently, some operate this type of air conditioning system by cycling the compressor clutch on and off. But these systems account for only a few variables for air conditioning passenger comfort and so have a fairly limited temperature range that the refrigerant is allowed to fluctuate within. Thus, maximum fuel efficiency is not obtained. Moreover, the life of the compressor clutch may be greatly diminished due to a high level of compressor on/off cycling.